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CdS, Cd0.98Gd0.02S, and Cd0.96Gd0.04S quantum dots (QDs) have been fabricated by solvothermal method and found to form in cubic phase. Raman spectra displayed first as well as second order longitudinal modes of CdS QDs. Transmission electron microscopy images depict the nearly spheroid particles of size in the range of 3.8–6.2 nm. Reflectance spectra showed that the absorption edge of the Cd0.98Gd0.02S and Cd0.96Gd0.04S QDs was red-shifted compared to that of CdS QDs. Electron paramagnetic resonance spectra of Cd0.98Gd0.02S and Cd0.96Gd0.04S reveal resonance signals at g ≈ 2.16 and 2.93 corresponding to the gadolinium (III) ions located at sites with frail as well as intermediate crystal field. Exploration of the magnetic property reveals that the Cd0.98Gd0.02S and Cd0.96Gd0.04S QDs show signs of superparamagnetism. The photocatalytic activity of CdS and Cd0.96Gd0.04S QDs was studied on malachite green oxalate dye under artificial solar light irradiation. The decomposition rate of CdS and Cd0.96Gd0.04S QDs evaluated on the malachite green oxalate dye is as follows: Cd0.96Gd0.04S > CdS.

Pristine and Co-doped ZnS quantum dots (QDs) were fabricated via a hydrothermal technique. Morphology studies showed that the fabricated QDs were nearly spheroidal with narrow size distribution. X-ray diffraction and Raman spectroscopy analyses demonstrated that the Co ions effectively penetrated the host matrix without changing its cubic phase. A minimal blue shift was found in the pristine ZnS QDs after doping with Co. The pristine and Co-doped samples exhibited similar blue emission, while increased (two times) photoluminescence intensity was observed for the Co-doped sample. X-ray photoelectron spectroscopy analysis showed trivalent Co ions in the ZnS lattice. The diamagnetic ZnS QDs were turned into ferromagnetic through Co-doping. The Co-doped ZnS QDs portrayed higher photocatalytic degradation (PCD) of Rhodamine B dye under artificial solar simulator irradiation than pristine ZnS. Hence, the Co-doped ZnS QDs may find applications in luminescent, spintronic and photocatalytic devices.

CdS and CdS:Eu quantum dots (QDs) with relatively uniform size and a narrow size distribution were fabricated by a solvothermal method. X-ray diffraction and Raman spectroscopy analyses revealed that the synthesized samples were polycrystalline with a cubic structure. An almost spheroidal morphology with slight polydispersity was observed in both low and high-resolution transmission electron microscopy images. The optical band gap of the CdS and CdS:Eu QDs was found to be 3.1–3.3 eV. An X-ray photoelectron spectroscopy analysis disclosed the existence of Eu with a trivalent state and the obtained composition values are nearer to stoichiometry. The CdS:Eu QDs displayed room-temperature ferromagnetism. The CdS:Eu QDs showed enhanced photocatalytic activity compared to CdS during malachite green oxalate dye degradation under artificial solar illumination. Hence, Eu doping is a promising path for facilitating better photocatalytic activity and ferromagnetism of CdS.

The tunable room-temperature ferromagnetism (RTFM) of ZnO nanoparticles through Dy doping were fabricated through a simple co-precipitation method for spintronic device applications. The synthesized samples were analyzed by studying their structural, morphological, optical, chemical, and magnetic properties. X-ray diffraction, selected area electron diffraction, and X-ray photoelectron spectroscopy results display that the Dy3+ have successfully entered for a few of the Zn2+ as a substitute in the ZnO crystal lattice without altering their hexagonal structure. Morphology studies of the suspensions consist of monodisperse and slightly hexagonal shaped nanoparticles. The tunable optical band gap was observed in the ZnO samples via Dy doping, confirmed by diffuse reflectance spectroscopy studies. Declaration of RTFM of the ZnO:Dy has been established with the noticed hysteresis in M–H loops and these studies indicate that the saturation magnetization of the ZnO sample as a function of Dy content. Amalgamating with the above results, it is suggested that, the observed RTFM in the ZnO:Dy nanoparticles may be interpreted by the contribution of the magnetic moments from the unpaired 4f electrons of Dy3+ ions.

Dilute magnetic semiconductors with extended ferromagnetic properties are heavily sought for use in next-generation spintronic devices. In this work, we show that co-doping 3 at% Al into Zn 0.44 Gd 0.03 O 0.50 nanoparticles can change their magnetic nature from weak to well-defined ferromagnetism (FM) at room temperature. X-ray diffraction (XRD), selected area electron diffraction (SAED), and Raman spectroscopy show that the Gd and Al atoms replaced the Zn atoms in the ZnO crystal lattice without forming other impurity phases. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses of the suspensions revealed the high crystallinity and monodispersity of the 34–44 nm nanoparticles. The undoped and Gd-doped ZnO samples showed diamagnetism and weak FM, while the (Gd, Al) co-doped samples exhibited robust room temperature FM. The enhanced FM of the Zn 0.44 Gd 0.03 Al 0.03 O 0.50 sample can be achieved by increasing the carrier concentration via Al co-doping.

Impurity free cobalt 3d and erbium 4f co-doped ZnS nanoparticles (NPs) were synthesized using a chemical reflux technique. The as-synthesized NPs exhibited high crystallinity and a narrow particle-size distribution. X-ray diffraction and optical analysis showed that cobalt (II) and erbium (III) ions substituted the zinc (II) ions in tetrahedral sites. The tunable bandgap for ZnS NPs was attained through mono- and co-doping. The cobalt and erbium co-doped NPs displayed a robust magnetization with an enhanced coercivity at room temperature compared with the cobalt-doped ZnS NPs; this was due to the exchange interaction between the cobalt (II) electrons as well as the localized carriers incited through the erbium (III) co-doping. The sense captured with the regulating bandgap and ferromagnetic property in a single substance opens a new platform for advanced applications in optoelectronics and spintronic devices.

This paper reports the structural as well as the magnetic properties of ZnS:Eu 3+ (0, 1, 2, 3, and 4 at%) nanoparticles prepared by a hydrothermal method. The compositional, structural and magnetic properties of ZnS:Eu 3+ nanoparticles were investigated by energy dispersive X-ray spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM) measurements. XRD studies confirmed that all the samples had a cubic structure with good crystallinity. TEM showed that the particles were polycrystalline with a mean size of 5–8 nm. XPS revealed the oxidation state of the Eu in the ZnS lattice to be +3. All the Eu 3+ -doped ZnS nanoparticles exhibited room temperature ferromagnetic behavior as a function of doping concentration. The observed RTFM may be interpreted by the contribution of the magnetic moments from the unpaired 4 f electrons of Eu 3+ in the ZnS:Eu 3+ nanoparticles. The interesting magnetic properties of ZnS:Eu 3+ nanoparticles may be further explored for new generation spintronic devices.

The present study describes the elemental and structural as well as the room temperature magnetic properties of pure ZnS, Zn0.96Eu0.04S, and Zn0.95Eu0.04Tb0.01S NPs. The energy dispersive X-ray spectroscopy (EDAX) perceived the existence of zinc, terbium, europium, and sulfur in the prepared samples in expected stoichiometry ratio. X-ray diffraction (XRD) studies revealed that all the prepared NPs had a cubic structure. Transmission electron microscopy (TEM) studies showed the creation of wispy particles with an average size in the range of 5–8 nm. Magnetization (M) versus applied magnetic field (H) studies indicated that the pure ZnS NPs exhibited diamagnetic behavior, whereas both Zn0.96Eu0.04S and Zn0.95Eu0.04Tb0.01S NPs evinced the ferromagnetic nature at room temperature. However, suppression in ferromagnetism was observed in Zn0.95Eu0.04Tb0.01S compared to Zn0.96Eu0.04S nanoparticles due to the interactions between the Eu–Eu ions, Tb–Tb ions, and Eu–Tb ions. The above experimental results suggesting that both doped and co-doped ZnS nanoparticles are useful for spintronic device applications.

The compositional, structural, optical and magnetic properties of ZnS , Zn 0.98 Co 0.02 S, Zn 0.98 Sm 0.02 S and Zn 0.96 Co 0.02 Sm 0.02 S nanoparticles synthesized by a hydrothermal method are presented and discussed. X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies revealed that all the samples exhibited cubic structure without any impurity phases. X-ray photoelectron spectroscopy (XPS) results revealed that the Co and Sm ions existed in +2 and +3 states in these samples. The photoluminescence (PL) spectra of all the samples exhibited a broad emission in the visible region. The room temperature magnetization versus applied magnetic field ( M – H ) curves demonstrated that the Sm+Co doped nanoparticles exhibited enhanced ferromagnetic behavior compare to Co and Sm individually doped ZnS nanoparticles, which is probably due to the exchange interaction between conductive electrons with local spin polarized electrons on the Co 2+ or Sm 3+ ions. This study intensifies the understanding of the novel performances of co-doped ZnS nanoparticles and also provides possibilities to fabricate future spintronic devices.

Cr (0, 3 and 5 at.%) doped ZnS nanoparticles were successfully synthesized by hydrothermal method using PVP as capping agent. The influence of Chromium doping on the structural, luminescence and magnetic properties of ZnS nanoparticles is investigated. EDS spectra confirmed the presence of zinc, chromium and sulfur in the doped samples in near stoichiometric ratio. XRD and Raman analysis demonstrated successful incorporation of Cr3+ ions into ZnS lattice with the absence of metallic clusters or precipitates. TEM micrograph indicated that the particles were a few nm (